(425i) In situ Observations of Dynamics of Active Braze Joining

Brazing is an important joining technology for manufacturing hermetic seals between ceramic and metal surfaces. Active braze alloys make use of an active element such as titanium or zirconium that reacts with the ceramic to form an interfacial layer which improves the wettability of the metal alloy on the ceramic. The process of brazing is a complex competition between thermal transport, phase changes and chemical reactions between the molten braze and the bonding surfaces. Most active brazing operations take place at high temperatures up to 1000°C which makes studying defect formation and troubleshooting the mechanisms quite challenging. Literature studies of brazing have traditionally relied primarily on post mortem analysis of final joints to investigate the braze process. Recently, we have developed a method to visualize the dynamics of an active brazing process in situ. By substituting optically transparent sapphire for traditional alumina ceramic substrate, the braze alloy can be observed during joining within a high temperature vacuum chamber. We have successfully demonstrated the experiment with a silver-zirconium active braze alloy. Several interesting dynamics have been observed including phase transitions and wetting phenomena. We will compare in situ images with traditional post mortem analysis of the final joints.

Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.